A Nonparametric Approach to QT Interval Correction for Heart Rate

Cardiac Conduction Model for Generating 12 Lead ECG Signals With Realistic Heart Rate Dynamics

We present an extended heterogeneous oscillator model of cardiac conduction system for generation of realistic 12 lead ECG waveforms. The model consists of main natural pacemakers represented by modified van der Pol equations, and atrial and ventricular muscles, in which the depolarization and repolarization processes are described by modified FitzHugh-Nagumo equations. We incorporate an artificial RR-tachogram with the specific statistics of a heart rate, the frequency-domain characteristics of heart rate variability produced by Mayer and respiratory sinus arrhythmia waves, normally distributed additive noise and a baseline wander that couple the respiratory frequency. The standard 12 lead ECG is calculated by means of a weighted linear combination of atria and ventricle signals and thus can be fitted to clinical ECG of real subject. The model is capable to simulate accurately realistic ECG characteristics including local pathological phenomena accounting for biophysical properties of the human heart. All these features provide significant advantages over existing nonlinear cardiac models. The proposed model constitutes a useful tool for medical education and for assessment and testing of ECG signal processing software and hardware systems.

Impact of Age and Sex on QT Prolongation in Patients Receiving Psychotropics

OBJECTIVE

To assess older age and female sex, 2 of the major risk factors for potentially fatal cardiac arrhythmias or sudden cardiac death in patients prescribed psychotropics, within the context of electrocardiographic evidence of time between start of Q wave and end of T wave (QT) interval prolongation, which is an indicator of an increased risk for potentially fatal cardiac arrhythmias.

METHOD

The literature on the relation between age, sex, and QT interval with respect to psychotropic drugs was reviewed.

RESULTS

The QT interval must be corrected (QTc) for heart rate. Because slower heart rates prolong and faster heart rates shorten the QT interval, people with faster heart rates may have a prolonged QT interval that is not apparent until the correction is performed. QTc values for apparently healthy post-pubertal people are less than 450 ms for males and less than 470 ms for females. The longer QT intervals in women may account for their increased risk of potentially fatal cardiac arrhythmias on psychotropics. QTc increases with increasing age. Assessment of QTc in older people is especially important to identify people with a longer QTc who are more likely to attain a serious QT level with drugs that prolong QTc. The age-related increase in QTc is more evident in men than women, suggesting that male sex does not afford protection against potentially fatal arrhythmias at older age.

CONCLUSION

The association of increasing age and female sex with greater QT intervals indicates the need to have an increased awareness of the QTc prior to use of these psychotropics and to evaluate the QTc after initiation of therapy.